The natural draft cooling tower is open and consists of a direct-contact system. These towers are build-up with a magnified shell-shaped structure. They often bear to harsh environments that can lead to a severe concrete slump.
This tower is mainly used in power stations and found in energy-intensive facilities such as oil refineries, natural gas plants, and petrochemical plants. The role of this tower is to remove the heat from the circulating water system. This tower is shaped in such a way that it can draw a natural draft into the building.
The Drawback of its Lifespan
An assessment was made to know the main reason behind the deterioration. By boiling down their structural integrity and flourishing a repair strategy would give the design a boosted life of 25 years.
It was found that the aged structure was quickly crippling by chloride-induced corrosion, and just repairing the concrete would not help to extend its service life. As a result, to upgrade the cooling tower, you can design and install a custom electronic protection system that can give long-term corrosion solutions.
In this article, we have highlighted information about sustaining the natural draft cooling tower for at least 25 years. Let’s get started.
Repair and construction
The main aim was to extend the service life of the natural draft cooling tower for at least 25 years while focusing on its safety, cost, and durability without changing its design. To achieve this, the cooling tower suppliers were allowed to take some time and came up with as many of the repairs as feasible while minimizing the downtime.
There was massive damage in the upper section of the tower shell. So, it was decided to demolish and reconstruct the surface above the throat. Meanwhile, the partial depth concrete repairs at both the interior and exterior of the shell were chosen on the opposite half of the surface, below the neck, where the concrete degradation was less severe.
It was discovered that X-columns in their current damaged state have sufficient capacity, and they do not require restoration to their previous state. Thus, X-columns were repaired to maintain the current structural power for a longer duration.
Cathodic Protection Design and Installation: Hybrid Cathodic Protection Scheme
Industrial cooling tower manufacturers in India have come up with two different protection schemes to maintain the tower. One is cathodic protection (CP) that was selected as a reliable and adaptable repair strategy to protect the tower shell and X-column from continued deterioration.
The second is impressed current cathodic protection (ICCP). This was selected for shell based on the ability to control the voltage levels at different locations of the large shell for the service life span.
There were three types of ICCP systems, and each of them was used on different sections of the shell.
- Ebonex discrete titanium suboxide ceramic tube anodes – These were used in the heavily reinforced, thickened concrete base of the shell.
- Mixed metal oxide coated titanium ribbon mesh anodes – These anodes were grouted into the slots to cover concrete for protecting the repair height of the existing shell.
- Mixed metal oxide coated titanium ribbon mesh anodes – These anodes were cast between the reinforcing layers in the reconstructed portion of the shell above the throat to prevent corrosion.
Moreover, vector corrosion services (VCS) monitored each vertical stack and were controlled by rectifiers. VCS remote monitoring services’ (RMU) were located on the canopy walkway. Measurement of the voltage, current, and potentials can be known by RMU web-based software. Four out of thirty-two X-columns were also instrumented and connected into the VCS to keep all the measurements in check.
Galvanic Cathodic Protection (GCP) via galvanic jackets was selected for the X-columns based on the durability of its components within the harsh basin environment. The Galvanic jackets come with alkali-activated distributed zinc anodes. They were installed with cement mortar inside stay-in-fiber reinforced polymer (FRP) forms.
These jackets are essential because they operate low-voltage batteries supplying protective current to the column reinforcing steel. They do not require any maintenance or monitoring to provide long-term corrosion protection. These jackets are suitable for use in wet environments and can be installed without external lead to wiring failures.
Keeping all the services of a natural draft cooling tower in check is crucial as it plays an essential role in our society. Some advantages of this tower include power savings due to the absence of electrical fans, no corrosion problems, low maintenance, and no recirculation of air as the stack outlet is located high up.
Hence, above was everything regarding a complete design building to address the corrosion of the reinforcing steel inside the natural draft cooling tower. Thus, according to building guidance, the cooling tower will now have a lifespan of 25 years.